This invention relates to an x-ray analysis system and more particularly to x-ray optics for measuring asbestos within air samples.
Heretofore analysis of elements, samples of materials, crystals, etc., have been carried out by x-ray diffraction since it is well known that different material have characteristic x-ray patterns. Most fibers other than asbestos are single crystals with a major axis along the fiber direction. Preferred orientation is observed for planes normal to the fiber axis but not for planes parallel to the axis. Thus the measurement of asbestos fibers is very difficult especially in a mixed sample.
One factor which makes measurement of asbestos difficult is that the quantity which can be collected from a reasonable amount of air is far too small to measure with x-ray film cameras. Therefore diffractometers with electronic detectors are required, however other problems are introduced because of the peculiar morphology of crystalline matter. Chrysotile asbestos, like all crystals, has a characteristic x-ray diffraction pattern. However, platy serpentine has almost exactly the same x-ray pattern as chrysotile and many other clay minerals have very similar patterns. It has been determined that the morphology of chrysotile asbestos is like that of a "rolled up" sheet of crystalline matter with the a-axis parallel to the fiber axis, the c-axis is nearly perpendicular to the "tubular" wall, with the b-axis perpendicular to the a and c axis. Thus, the axes (b and c) take different orientations depending on where on the fiber they are set up. Preferred orientation can be observed from the planes parallel to the fiber axis using the well-known techniques photographic, however such methods cannot be adapted to airborne asbestos samples since it is not possible to form the fibers in the required small oriented bundles. Further, it has been determined that even with an oriented sample in a standard diffractometer system the major crystal plane (002) diffracts equally well for all orientations. Therefore well known x-ray optics cannot be used for detecting asbestos in mixed samples. A suitable system has been set forth in a publication NRL Report 7874, QUANTITATIVE ANALYSIS OF AIRBORNE ASBESTOS BY X-RAY DIFFRACTION, by L. S. Birks, M. Fatemi, J. V. Gilfrich and E. T. Johnson, Naval Research Laboratory, Washington, D.C. 20375, which forms a part of this specification.